Young Dusty Starburst Galaxies at z 2 Tohoku University, - - PowerPoint PPT Presentation

▶
young dusty starburst galaxies at z 2
SMART_READER_LITE
LIVE PREVIEW

Young Dusty Starburst Galaxies at z 2 Tohoku University, - - PowerPoint PPT Presentation

Jan 10, 2023 292 likes •395 views

Young Dusty Starburst Galaxies at z 2 Tohoku University, Astronomical Institute Tomohiro Yoshikawa, MODS team Cosmic SFR Density Cosmic History of SFR Density cosmic SFR density has its peak at z 2 and monotonically decays from z

slide-1
SLIDE 1

Young Dusty Starburst Galaxies at z 〜 2

Tohoku University, Astronomical Institute Tomohiro Yoshikawa, MODS team

slide-2
SLIDE 2

2

Cosmic SFR Density

Cosmic History of SFR Density

cosmic SFR density has its peak at z 〜 2 and monotonically decays from z 〜 1 to the present universe. What populations do contribute to the star formation at the star-forming epoch of the Universe?

0.1- 0.01-

SFR Density (M◎yr-1Mpc-3)

  • 0.1
  • 0.01

(Caputi et al. 2007)

slide-3
SLIDE 3

3

Present Samples (○) on BzK diagram

Spectroscopic Observation of Galaxies at z 〜 2

Observation of Hα Emission Lines

Star Formation Rate Indicator Spectroscopic Redshift

Sample Selection

Star-Forming BzK designed to select z=1.4-2.5 MIPS+sBzK S24>80μJy: ULIRGs at z ～ 2 Near-infrared spectrograph is suitable to study star-forming galaxies at z~2 → Subaru/MOIRCS !

difficult for

  • ptical

instruments previous studies (e.g., BX/BM and DRGs) are biased by attenuation/age

slide-4
SLIDE 4

4

Data

Star-Forming BzK galaxies

K-selected star-forming galaxy at z~2 (MOIRCS Deep Survey field) with Ks < 23 (AB) S24 > 80μJy: 18 S24 < 80μJy: 21 X-ray galaxies (Alexander et al. 2003) are excluded. Observation Subaru/MOIRCS MOS mode 4 masks (CDFN1-4) exposure time: 160-320 min HK500 grism + 0.8”slit: R~500

※ serendipitous target of Akiyama et al.

HDF-N

39 galaxies in total

slide-5
SLIDE 5

5

Hα Emission Lines

Hα Detection Rate

  • bs.

rate 26 15 58% 13 8 62% total 39 23 59% Hα S24>80μJy S24<80μJy

Hα+[NII] Hα+[NII]

slide-6
SLIDE 6

6

redshift Hα Luminosity [erg/s] Star Formation Rate [L◎/yr] atmospheric absorption between H and K Extinction Corrected

Hα Emission Lines

Redshift Distribution

sBzK galaxies lie at 1.4<z<2.5 The galaxies without emission line detection have smaller SFR? expected detection rate is much higher (>85%), if all samples have similar SFR.

slide-7
SLIDE 7

7

SFR and Stellar Mass

Our Emission Line Galaxies

  • nly a weak correlation

between SFR and M★

Other Studies

Daddi+ 2007 (sBzK, rest-UV) strong correlation

  • ther studies using Hα

emission line also show week (shallower) correlation

M★ [M◎] LHα [erg/s]

A part of low mass galaxies have higher SFR

divide the samples into two groups with SSFR (■◇)

slide-8
SLIDE 8

8

Young Dusty Starburst Galaxies

mass-weighted age AV

■◇: this work

  • ○: BM/BX (Erb et al. 2006)

filled symbol: SSFR > 10-8 yr-1 ○: S24>80μJy

Large SSFR galaxies are young and dusty galaxies

Mass-Weighted Age and Extinction

A part of BM/BX galaxies (Erb et al. 2006) are also young but less attenuated. mid-infrared selected samples choose the young and dusty galaxies?

slide-9
SLIDE 9

9

Contribution to Cosmic SFR Density

SFR Density Estimated from Hα Luminosity

■ SSFR > 10-8yr-1: 0.105 M◎yr-1Mpc-3 ◇ SSFR < 10-8yr-1: 0.032 M◎yr-1Mpc-3

Low-mass young dusty galaxies significantly contribute to the cosmic SFR density

0.1- 0.01-

SFR Density (M◎yr-1Mpc-3)

  • 0.1
  • 0.01

(Caputi et al. 2007)

+0.020

  • 0.039

+0.015

  • 0.006
slide-10
SLIDE 10

10

Summary

We observed 39 sBzK galaxies and Hα emission lines are detected from 23 of them. Our emission line galaxies show only a weak correlation between stellar mass and star formation rate, owing to large specific SFR galaxies. Large specific SFR galaxies are young and dusty starburst galaxies with bright 24μm flux. Low-mass young dusty galaxies would significantly contribute to the cosmic SFR density at z ～ 2